This invention concerns an aluminum electrolytic capacitor containing a low-resistivity electrolyte consisting essentially of 6 wt % diammonium adipate, 3 wt % ammonium formate, 16 wt % water, 0.025 to 0.3 wt % ammonium dihydrogen phosphate, 1 to 10 wt % p-nitrobenzoic acid, and the balance, ethylene glycol.
Low-resistivity electrolytes are desirable to impart to the capacitor containing them low equivalent series resistance (ESR) at low temperatures, a low ESR ratio (the ratio of ESR at -40.degree. C. to that at room temperature), and low impedance at higher frequenices. If the capacitor is a low-voltage unit, the low-resistivity electrolyte also imparts low ESR at room-temperature.
Formate salts have been added to electrolytes to lower resistivities as formates are highly conductive. However, formates are derived from a fairly strong acid which will attack the dielectric oxide on aluminum foil electrodes. Therefore, formates are generally used with other conducting salts.
Water is frequently added to electrolytes to reduce resistivity in addition to aiding in the reformation of aluminum electrodes during capacitor use. Historically, however, large amounts of water were avoided as capacitor stability was impaired, and if even a few ppm of choride were present dielectric oxide could not be reformed and aluminum corrosion was accelerated.